Image forming apparatus having developer carrying member supplied with oscillating voltage

Abstract

An image forming apparatus includes an image bearing member for bearing an electrostatic latent image; developer carrying member for carrying a developer comprising toner particles; a voltage source for applying to the developer carrying member an oscillating voltage having a predetermined frequency; wherein the following is satisfied: |Vpp-2Vcont|/16Vf.sup.2 <d.sup.2 /|Q| where Vpp (V) is a peak-to-peak voltage of the oscillating voltage, Vf (Hz) is the frequency of the oscillating voltage, Vcont (V) is a potential difference between a voltage of a DC component of the oscillating voltage and a potential of an image portion on the image bearing member when a maximum image density is provided, Q (c/kg) is an average triboelectric charge amount of the toner particles, and d (m) is a gap between the image bearing member and the developer carrying member.

What is claimed is: 
     
       1. An image forming apparatus comprising: an image bearing member for bearing an electrostatic image;   a developer carrying member, opposed to said image bearing member, for carrying a developer comprising toner particles and carrier particles;   electric field forming means for forming an intermittently alternating electric field between said image bearing member and said developer carrying member by applying a substantially rectangular developing bias voltage to said developer carrying member, wherein the developing bias voltage has an oscillating portion having a continuous plurality of oscillating voltage levels and has a rest portion having a non-oscillating voltage level.   
     
     
       2. An apparatus according to claim 1, wherein said image bearing member is disposed across a predetermined gap from said developer carrying member, said image bearing member contacting carrier particles formed into chains. 
     
     
       3. An apparatus according to claim 1, wherein said image bearing member comprises a photosensitive layer, and further comprising means for selectively exposing said photosensitive layer to a light spot that is turned on and off in accordance with an image signal. 
     
     
       4. An apparatus according to claim 3, wherein said image bearing member carries toner particles on the portion thereof which has been exposed to the light spot.